This invention relates generally to an apparatus and a process for the separation of solid particles from gases. More specifically, this invention relates to the separation of particulate catalyst materials from gaseous materials in an FCC process.
Cyclonic methods for the separation of solids from gases are well known and commonly used. A particularly well known application of such methods is in the hydrocarbon processing industry where particulate catalysts contact gaseous reactants to effect chemical conversion of the gas stream components or physical changes in the particles undergoing contact with the gas stream.
The FCC process presents a familiar example of a process that uses gas streams to contact a finely divided stream of catalyst particles and effects contact between the gas and the particles. The FCC processes, as well as separation devices used therein are fully described in U.S. Pat. No. 4,701,307 B1 and U.S. Pat. No. 4,792,437 B1, the contents of which are hereby incorporated by reference.
Efficient separation of particulate catalyst from product vapors is very important in an FCC process. Particulate catalyst that is not effectively separated from product vapors in the FCC unit must be separated downstream either by filtration methods or additional separation devices that multiplicate separation devices utilized in the FCC unit. Additionally, catalyst that is not recovered from the FCC process represent a two-fold loss. The catalyst must be replaced, representing a material cost, and catalyst lost may cause erosion to downstream equipment. Severe erosion may cause equipment failure and subsequent lost production time. Accordingly, methods of efficiently separating particulate catalyst materials from gaseous fluids in an FCC process are of great utility.
In the FCC process, gaseous fluids are separated from particulate catalyst solids as they are discharged from a reaction conduit. The most common method of separating particulate solids from a gas stream uses centripetal separation. Centripetal separators are well known and operate by imparting a tangential velocity to gases containing entrained solid particles that forces the heavier solids particles outwardly away from the lighter gases for upward withdrawal of gases and downward collection of solids.
U.S. Pat. No. 4,397,738 B1 and U.S. Pat. No. 4,482,451 B1 disclose an arrangement for initial quick centripetal separation that tangentially discharges a mixture of gases and solid particles from a central reaction conduit into a containment vessel. The containment vessel has a relatively large diameter and generally provides a first separation of solids from gases. In these arrangements, the initial stage of separation is typically followed by a second more compete separation of solids from gases in a traditional cyclone vessel.
Another method of obtaining this initial quick separation on discharge from the reaction conduit is disclosed in U.S. Pat. No. 5,584,985 B1. This patent discloses the contacting of feed and catalyst particles in a riser conduit. The exit from the riser conduit comprises an arcuate, tubular swirl arm which imparts a swirling, helical motion to the gases and particulate catalyst as they are discharged from the riser conduit into a separation vessel. The swirling, helical motion of the materials in the separation vessel effect an initial separation of the particulate catalyst from the gases. The swirl motion of the mixture continues while it rises up the gas recovery conduit. At the end of the gas recovery conduit, the mixture is drawn into cyclones to effect further separation of the particulate catalyst from the gases. This arrangement is known as the UOP Vortex Separation System (VSSSM).
Cyclones for separating particulate material from gaseous materials are well known to those skilled in the art of FCC processing. Cyclones usually comprise an inlet that is tangential to the outside of a cylindrical vessel that forms an outer wall of the cyclone. In the operation of an FCC cyclone, the entry and the inner surface of the outer wall cooperate to create a spiral flow path of the gaseous materials and catalyst that establishes a vortex in the cyclone. The centripetal acceleration associated with an exterior of the vortex causes catalyst particles to migrate towards the outside of the barrel while the gaseous materials enter an interior of the vortex for eventual discharge through an upper outlet. The heavier catalyst particles accumulate on the side wall of the cyclone barrel and eventually drop to the bottom of the cyclone and out via an outlet and a dipleg conduit for recycle through the FCC apparatus. Cyclone arrangements and modifications thereto are generally disclosed in U.S. Pat. No. 4,670,410 B1 and U.S. Pat. No. 2,535,140 B1.
U.S. Pat. No. 4,956,091 B1 discloses a separator comprising a swirl chamber that imparts a swirl motion to a mixture of gases and solids in an angular direction. The mixture then enters a swirl tube through swirl veins which intensify the swirl motion of the mixture in the same angular direction to effect separation between the solids and gases. This same principle has been followed in vortex separation systems that are used in conjunction with cyclones. The angular direction of the swirl motion induced by the VSSSM has the same angular direction as the swirl motion induced by the cyclones. It was, perhaps, thought that consistency between the swirl motion in the VSSSM and the cyclones will operate to intensify the swirl motion in the cyclone and thereby effect greater separation.
U.S. Pat. No. 5,370,844 B1 and U.S. Pat. No. 4,364,905 B1 disclose cyclone inlets that radially extend from and communicate with a central gas recovery conduit. Radially extending cyclone inlets are the most common. However, cyclone inlets of which the long, straight sidewall is disposed just inwardly of a tangent to a central gas recovery conduit have been licensed for commercial use.
Another concern involved in arranging cyclones in a vessel is to provide clearance between cyclones to permit adequate access for installation and for maintenance purposes. Clearance between cyclones becomes a greater consideration when more cyclones are installed in a vessel.
Accordingly, it is an object of the present invention to improve the efficiency of separating particulate solids from vapors in an FCC unit. It is a further object of the present invention to further improve such efficiency of separation in an FCC unit that utilizes a VSSSM with one or more cyclones. An additional object of the present invention is to assure adequate clearance between cyclones in a containing vessel.
It has been discovered that by configuring an inlet to a cyclone so that a short side of the inlet to the cyclone is substantially tangential to a gas recovery conduit which transports a mixture of particulate material and gaseous fluids from a reactor conduit to the cyclone increases separation efficiency and also allows more cyclones to be installed in the containing vessel with greater clearance between the cyclones.
Accordingly, in one embodiment, the present invention relates to a process for the fluidized catalytic cracking of a hydrocarbon feedstock. A hydrocarbon feedstock and solid catalyst particles are passed into a reaction conduit to produce a mixture of solid catalyst particles and gaseous fluids. The mixture of the catalyst particles and gaseous fluids is induced to swirl to decrease the catalyst particle concentration and increase the gaseous fluids concentration in the mixture. The mixture is transported through a gas recovery conduit and passed to at least one cyclone through a cyclone inlet having a short side and a long side. The short side is substantially tangential to a cross-sectional profile of the gas recovery conduit. The mixture is induced in the cyclone to swirl to further decrease the catalyst particle concentration and further increase the gaseous fluids concentration in the mixture.
In another embodiment, the present invention relates to an apparatus for the fluidized catalytic cracking of a hydrocarbon feedstock comprising a reaction conduit for contacting a hydrocarbon feedstock and solid catalyst particles to produce a mixture of solid catalyst particles and gaseous fluids. A gas recovery conduit is in communication with the reaction conduit, and a cyclone is in communication with the gas recovery conduit. The cyclone has an inlet comprising a short side and a long side, and the short side is substantially tangential to a cross sectional profile of the gas recovery conduit.
In a further embodiment, the present invention relates to an apparatus for the fluidized catalytic cracking of a hydrocarbon feedstock comprising a reaction conduit for contacting a hydrocarbon feedstock and solid catalyst particles to produce a mixture of solid catalyst particles and gaseous fluids. A gas recovery conduit is in communication with the reaction conduit for transporting the mixture, and a cyclone is in communication with the gas recovery conduit. The cyclone has a curved outer wall and an inlet comprising a first side and a second side. A first side of the inlet is contiguous with the curved outer wall, and the second side of the inlet is substantially tangential to a cross sectional profile of the gas recovery conduit.
Additional details and embodiments of the invention will become apparent from the following detailed description of the invention.